Scientists studying climate change in Antarctica reported this week that a hole in the protective ozone layer of the Earth’s atmosphere has shrunk. The discovery of the hole in the 1980s led to a worldwide phasing out of ozone-depleting chemicals once used in products from hairspray to air conditioners. Alexandra Witze, reporter for “Nature” Magazine, joins Hari Sreenivasan from Denver to discuss.

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HARI SREENIVASAN, PBS NEWSHOUR WEEKEND ANCHOR:

Scientists studying climate change in Antarctica reported this week that the hole in the protected ozone layer of the earth's atmosphere has shrunk. The discovery of the hole in the mid-1980s led to a worldwide facing out of ozone-depleting chemicals known as chlorofluorocarbons, which had been used in products ranging from hairspray to air conditioners.

Joining me now from Denver to discuss how that policy has worked and how the hole is healing is Alexandra Witze, a reporter for "Nature Magazine".

So, I guess the first thing is, is that this is sort of a success story. I mean, humanity actually together, did something and that we're seeing some results.

ALEXANDRA WITZE, NATURE MAGAZINE:

Yes, it's a pretty rare environmental success story. I mean, you can say that we caused the problem in the first place by emitting all these chemicals, but the world basically got together and in 1987, put together a global treaty called the Montreal Protocol that essentially banned these chemicals that had been chewing away at the ozone layer.

So, yes, it's good news. It's a good story for once in the environment.

HARI SREENIVASAN:

And this — I should be sure to mention that this doesn't mean that everything is fixed. This is a long slow process. They're just finding that it's gotten better.

ALEXANDRA WITZE:

Sure. What the scientists announced this week is that year over year, on average, the ozone hole is getting just a little bit smaller every year. From 2000 to 2015, it shrank by 4 million square kilometers over that whole period. It doesn't sound like a whole lot, but it means that overtime, this opening that is letting all these nasty ultraviolet radiation is gradually shrinking and that's good news for us here in earth.

HARI SREENIVASAN:

This is the hole that they measure is primarily over the South Pole. The ozone layer, of course, is over the entire planet, right?

ALEXANDRA WITZE:

Yes. So, ozone is kind of like a protected shield in the upper atmosphere. You can think of it like a blanket enveloping the earth and protecting us from these ultraviolet rays. What happens is these chemicals that are emitted get caught up into the upper atmosphere and they get transported towards the Polar Regions. And over the South Pole, they start to trigger these chemical reactions that chew away at this protected blanket.

So, even though ozone is all around the planet, and even though we're emitting stuff, you know, around cities, what happens is these chemicals get transported down to the South Pole. And so, that's where we see the hole opening up every year.

HARI SREENIVASAN:

And last year, or maybe it was a year before, I can't remember, some volcanic eruptions actually had a negative impact on this. So, even though we weren't cranking out the hairspray cans, the earth still has the ability to disrupt the ozone layer.

ALEXANDRA WITZE:

Yes, this was one of the really puzzling things last year. In October, scientists saw one of the biggest ozone holes on record, and they didn't really understand why, because we've been phasing out these chemicals and everything seemed to be on track to healing. It turned out it was a volcano to blame. There was an eruption in Chile in April of last year, and basically, the particles that this eruption put out go into the upper atmosphere and they also start to trigger the same ozone-destroying reactions.

So, even though we've been cleaning up our act, volcanoes can still get in there and cause trouble as well.

HARI SREENIVASAN:

It seems that perhaps it's the narrow focus of the chemicals in terms of why this worked. I mean, because a lot of people will ask, well, why can't humanity get together like this around climate change and carbon emissions overall?

ALEXANDRA WITZE:

Yes, this was sort of a tractable problem, as environmental problems go. I mean, there is a huge industry, of course, that made these air conditioners and refrigerants that had these chemicals. But basically, technology came up with alternatives. And so, we were able to swap out the air conditioners and the refrigerants that had these nasty ozone-destroying chemicals with ones that didn't.

So, that was a fairly easy problem — not easy but a doable problem to solve. It's harder with greenhouse gasses and carbon pollution because they're so many sources, right? Power plants, deforestations, cement production. It's not just one thing to swap out for the climate change and carbon emissions.

So, that's — there might be lessons to learn, I think, from the ozone success story but it's going to be a lot bigger challenge with climate change.

HARI SREENIVASAN:

All right. Alexandra Witze from "Nature" — thanks so much for joining us.